I would use LabVIEW and the Vision toolkit.
This application actually has two major parts.
The first is locating the balls. You need to have bright lighting and a short shutter time to capture the images without much blurring. You can probably use pattern matching to locate each ball. A high frame rate camera would probably also help.
The second part is tracking the path of each ball. If there are a lot of balls, this could be difficult. You will probably have to come up with some algorithms to calculate the trajectory of each ball and predict where it is most likely to be in the next frame. Searching in this small area for the closest ball will be fairly easy. In some cases, you might have to skip a frame where there is some confusion, then come back to it after analyzing the next frame. If there are collisions between the balls, this will make it more difficult to trace them as well.
Bruce
Bruce Ammons
Ammons Engineering